With a gas turbo set comprising two gas turbines, a sequential combustion takes place, for which two e.g. annular combustion chambers and/or ring pipe combustion chambers are provided. One is arranged on the high pressure side and the other is arranged on the low pressure side. The combustion chamber on the high pressure side is supplied with compressed air, which is mixed with fuel and the mixture is ignited. Downstream of the high pressure combustion chamber is arranged a first gas turbine, a high pressure turbine, which is operated by the hot gases generated in the high pressure combustion chamber. Here the hot gases experience a partial cooling, but when leaving the high pressure turbine, nevertheless have a relatively high temperature, in the region between 900° C. and 1,400° C. for instance. A second low pressure combustion chamber is arranged downstream of the high pressure turbine which operates by auto-ignition and in which, in particular air not consumed in the first combustion chamber during combustion participates in a second combustion process. This low pressure combustion chamber essentially has the form of a gas-swept annular channel, into which fuel is injected. With a temperature of the exhaust gas from the high pressure turbine from 850° C., self-ignition of the injected fuel takes place in the low pressure combustion region, into which the second combustion process takes place in the gas turbo set. A second gas turbine, which is in particular a low pressure turbine, is arranged downstream of the low pressure turbine. It is important for the configuration of the low pressure combustion chamber for it to have an adequate length to ensure that exhaust gases and fuel mix well and for it to stay sufficiently long in the combustion chamber for complete combustion.
A gas turbo set of the type cited in the introduction emanates from the unexamined publication DE 44 22 701 A1 for instance. This unexamined publication describes a method for controlling the gas turbo set, in which a temperature of the exhaust gas from the first turbine is measured immediately ahead of the site of the auto ignition in the second combustion chamber and the fuel quantity for the different combustion chambers is controlled by the measured temperature.
A further gas turbo set can be inferred from the unexamined publication DE 42 32 383 A1, in which a screw-type swirl motion is imposed upon a gas flow in order to achieve a longer throughflow, or holding time in an annular combustion chamber between two turbines. To this end, the turbine located downstream of the combustion chamber has no first row of guide vanes so that the first row of guide vanes of this turbine is subjected to the swirl from the turbine arranged upstream thereof.
EP 0 646 705 indicates a gas turbo set comprising at least two turbines, which are arranged on a common shaft. Here the second downstream turbine is larger in volume than the first turbine.